1. Field of the Invention
The present invention relates to a camera calibration apparatus, and more particularly to a camera calibration apparatus which estimates the position and the direction of a camera from the positions of characteristic points of an image imaged.
2. Description of the Related Art
In a conventional camera calibration apparatus of the type mentioned, an object having three or more characteristic points (or characteristic lines) whose relative positions are known is imaged, and calibration wherein the position and the direction of the camera are estimated from the positions of the characteristic points in the thus imaged image is performed.
Conversely to the calibration described above, as an object posture estimation method, a tetrahedron arrangement estimation method which uses four or more characteristic points, a three-line segment and two-point arrangement estimation method which uses three or more line segments and two or more characteristic points, and so forth have been proposed. While any of the object posture estimation methods estimates the posture of an object, since the relationship between the camera and the object is relative, it is also possible to estimate the position or the direction of the camera using the method.
The tetrahedron arrangement estimation method is disclosed in Japanese Patent Laid-Open Application No. Heisei 1-232484, and the three-line segment and two-point arrangement estimation method is disclosed in Japanese Patent Laid-Open Application No. Heisei 2-51008.
In the conventional camera calibration described above, processing of mapping between characteristic points originating from an image and characteristic points of an original object imaged is required. In this instance, in order to raise the accuracy in calibration, it is necessary to increase the number of characteristic points. However, as the number of characteristic points increases, the mapping processing becomes less stable and more complicated.
Further, with the tetrahedron arrangement estimation method, the three-line segment and two-point estimation method and so forth as an object posture estimation method, it is difficult to stably extract four or more characteristic points (characteristic lines) depending upon imaging conditions. As a result, even if an error occurs with the mapping between characteristic points, no countermeasure to correct the error can be taken.